The one on the left looks like the e-brake. The middle and right side parts are the load sensing brake proportioning valve system. As the bed gets loaded it compresses the spring and the bed gets lower. The long arm goes up relative to the bed and more brake pressure goes to the rear wheels. Having said that, your proportioning valve setup appears to be all screwed up. The link (middle circle) should be vertical and the arm between the valve (right circle) and the link should be straight. Although, It could be that since you took the bed off, the rear is too light causing the link to go horizontal. So, I'll correct myself and say, that link (middle circle) should be vertical with the bed bolted on and the truck sitting on the tires on the ground. Was the truck lifted? That would explain why the arm is bent. It's a quick and dirty way to keep the valve in the correct position.
Also, it looks like the e brake cable of the left has been stuffed around with. looks like it should go under the spring not over the top.